From the publication DE 10 2008 046 988 A1 a reflectometer for characterizing materials with regard to at least one optical reflection characteristic is known. The reflectometer comprises an ellipsoid mirror within the first focal point of which a sample to be characterized is held by way of a sample holder. By way of the sample holder the sample can be rotated about an axis of rotation. The sample is irradiated through an opening in the ellipsoid mirror by way of a radiation source. The ellipsoid mirror maps the radiation reflected by the sample illuminated in the first focal point via an aperture located in the second focal point onto a detector disposed behind that. Subsequently, the measured data from the reflectometer are assessed for characterizing the sample.